India has a small network of narrow-gauge railways that are narrower than the 4 ft 8 1⁄2 in (1,435 mm) standard gauge. They are 1,000 mm (3 ft 3 3⁄8 in) metre gauge, 2 ft 6 in (762 mm) gauge and 2 ft (610 mm) gauge. Project Unigauge was started in 1991 that seeks to standardise the rail gauges in India by converting almost all of the narrow-gauge tracks to 1,676 mm (5 ft 6 in) broad gauge. Only the heritage railways and urban railways will not be converted to 1,676 mm (5 ft 6 in) broad gauge. As a result, the narrow-gauge tracks have been progressive reduced from approx. 29,000 route km at the start of Project Unigauge in 1991 to approx. 6,000 route km in 2016.
References
Narrow-gauge railways in India Wikipedia(Text) CC BY-SA